The word America is derived from the given name of Amerigo Vespucci (1454-1512). He was an Italian merchant and explorer-navigator who took part in early voyages to the New World (1499-1500, 1501-02).
America has two primary meanings:
(1) The Americas: the two continents located to the east of the Pacific Ocean and to the west of the Atlantic Ocean, namely North America and South America. Central America is often referred to as such, but strictly speaking it is a part of North America.
(2) The United States of America. See United States.
In the United States and other countries, America usually refers to the United States (as in the song "America the Beautiful") rather than to The Americas. In many of the rest of the countries of The Americas, America--or rather, the cognate words in Spanish or Portuguese--often refer to The Americas.